1. Field of the Invention
This invention relates to a process and a device for the removal of solid or liquid particles contained in suspension in a gas flow.
2. Discussion of the Background
Devices for the removal of particulate matter from gas flows with the aid of electric fields (so-called electrofilters) are well-known in a variety of different forms. They are all based on the principle that the particles suspended in the gas flow are first in some way charged electrostatically in a unipolar manner (usually according to the principle of the corona effect), in order to be then attracted to the oppositely charged electrode (collecting electrode) and retained there. The final removal (withdrawal) of the particle layer deposited on the collecting electrode usually occurs periodically in a mechanical manner by rapping or vibrating the collecting electrode which is usually plateshaped. (cf. Leuger, Lexikon der Technik, Vol. 6, Energietechnik und Kraft-maschinen, key word "electrofilter", pp. 286-282 Stuttgart, 1965).
The continued development of electrofilters has led to numerous refinements of the device and modes of operation which have resulted to a certain extent in rather complicated and costly designs. Mention can be made here of the spatial and functional separation of the ionization source and the electric field for particle separation, use of additional electrodes (cf. DE-PS No. 24 38 670 and DE-OS No. 27 44 556), particle agglomeration (e.g. DD-PS No. 144 509; EP-A No. 0 009 857), pulsed electric fields (DE-OS No. 3 004 474 A1), installation of meshes in front of the collecting electrode (JP-Pat. No. 56-136668), alternating voltage operation with an insulating screen for the purpose of increasing the breakdown voltage (DE-OS No. 3 039 639), combination of electrofilters and cyclones (DE-OS No. 3 235 953 A1).
Despite the above-mentioned refinements and the resulting partial improvements, the conventional processes and devices for particle removal by means of electric fields leave much to be desired. Electrofilters are bulky and seldom possess the desired optimum efficiency. During rapping and vibrating of the collecting electrodes, part of the particles already separated are stirred up again and reentrained into the gas stream. The particle layer already deposited on the electrode is charged, whereby electrical breakdown with "back corona effects" can occur, and a fraction of the particles is thrown back into the gas stream. Further, the electric field strength, which is the determining factor in the separation of the particles, is limited since the breakdown voltage resulting from an inhomogeneous field distribution is considerably less than that for a homogeneous field. All these factors lead to a decrease in the filter efficiency and to a deterioration of particle separation.
Thus there is a great need to improve, refine, and reduce the cost of conventional electrofilter technology.